The proliferation of lightweight, portable computing devices and high-speed wireless local area networks (LANs) has enabled users to remain connected and be able to compute while on the move inside buildings and on campus areas around buildings. This new paradigm has given birth to a new class of applications that are “location aware.” The goal of mobile computing in many instances is to enable a user to interact effectively with his or her physical surroundings. One example of such an interaction is to track physical locations of network users, particularly mobile users. Doing so allows one network user to query the network for a location of another network user and to receive a reasonably accurate response.
One component of these systems is the actual tracking system, which determines the user's location. The Global Positioning System (GPS) is one example of a technology, which enables the creation of inexpensive and portable systems that can help locate and track users. GPS systems currently are used to provide direction to drivers through an in-vehicle system; provide location and tracking information for marine navigation; and allow shipping companies to locate and track individual shipments. However, the GPS system relies on an unobstructed view of several satellites, making its use for tracking users who are indoors ineffective.
To overcome this obstacle, alternate technologies have been developed to locate and track users or objects in an indoor environment. One such system uses tags placed on the items that are to be tracked. In an electronic sense, the tags can be either active or passive, and they communicate with base stations. The base stations are physically linked together through a wired or wireless network. Each tag transmits a unique code to identify itself. The location of the tag can thereby be determined to be in the vicinity of the base station with which the tag last communicated.
Such tag-based tracking and location systems require a significant installation of specialized base stations. A tag-based system can only determine the location of the tags as being “near” a particular base station. As a result, a large number of base stations must be installed to achieve a sufficiently high resolution. Furthermore, obtrusive tags have to be placed on every item that is to be tracked or located, and in the case of infrared tags, the system operates only when there is a line of sight between the tag and a base station. For these reasons, tag-based systems have shown very limited success.
Another technology has been developed which uses radio frequency transmissions from base stations and mobile units to track the location of mobile units. This technology is described in U.S. patent application Ser. No. 09/513,155, entitled “Using a Derived Table of Signal Strength Data to Locate and Track a User In a Wireless Network, and in U.S. patent application Ser. No. 09/513,355, entitled “Locating and Tracking a User in a Wireless Network Through Environmentally Profiled Data.”
In this system, a Wireless Local Area Network (WLAN) is utilized for locating and tracking users. A WLAN consists of base stations connected to a wired network, and mobile devices that are “connected” to the WLAN through radio frequency signals with the base stations. The signal sensing ability of both the base station and the mobile device are used to determine the location of the mobile device, and thus the location of the user of the mobile device. In particular, the strength of the signals received from several base stations is measured by the mobile device. The mobile device then compares the signal strength from each of the base stations to a pre-computed table containing the base stations' signal strength at various known locations of the mobile device. From this comparison, the mobile device determines its location. Alternatively, the signal strength from the mobile device can be measured at a number of base stations. This signal strength is then compared by a central computer to a pre-computed table containing the mobile computer's signal strength at the base stations for various known locations. From this table, the central computer determines the location of the mobile computer.
Although the mobile computer can identify its location using this system, a problem remains as to how one user, say User A, who is logged onto a network on a fixed or mobile computer can locate another mobile computer or, more likely, the person using the mobile computer, say User B. This problem has been solved for finding stationary users, since the requesting user, User A, can simply determine the location of a network access point to which the stationary user's, User B's, computer is connected and use that location to infer his or her location. But since, by definition, a mobile user can be physically located virtually anywhere within the coverage of the network, the problem becomes significantly more difficult to solve.
Yet another problem exists when one user is logged onto more than one computer in a network. Current systems and methods don't allow for distinguishing between the computers to identify where the user may be physically located.